I wouldn't be quick to rule FR out. Initially when they started flights they were restricted to 156pax but after a while this increased to 186. Yes performance wise the bigger runway would be useful but for the routes they operated to mainland UK it worked. During the period they operated the loads on the flights increased to good levels with exception of prestwick.
Now yes if the runway was extended great they would operate sun routes etc but now just throwing an idea out there, would perhaps the runway extension issues be a great excuse to blame/use when initial airport deals run out?
Only a suggestion/idea.
Regards